The present invention generally relates to contrast media formulations and, more particularly, to nonionic x-ray contrast media formulations, radiological compositions containing such formulations and methods for x-ray visualization utilizing such compositions.
The search for ideal contrast media for X-ray radiodiagnostic studies has extended over many decades. Bismuth subnitrate was the first radiocontrast agent used for visualization of the alimentary tract. Later, barium sulfate, a safer agent, was introduced. Barium sulfate has remained the most widely used radiographic agent for the alimentary tract (W. H. Strain, International Encyclopedia of Pharmacology and Therapeutics, Section 76, Vol. 1, Radiocontrast Agents, Chapter 1, Historical Development of Radiocontrast Agents, 1971, Pergamon Press). The inorganic, insoluble oral agents like bismuth subnitrate and barium sulfate serve as valuable tools for gastrointestinal radiodiagnosis.
Unlike gastrointestinal radiodiagnosis, urographic and angiographic X-ray procedures, require intravascular administration of a safe, water-soluble, radiopaque contrast medium. Since the introduction of the water-soluble ionic triiodobenzoic acid derivatives, such as diatrizoic acid and iothalamic acid, in the early 1960's, radiographic visualization of the vascular system has become the most important application of X-ray contrast media. These X-ray procedures are valuable in the diagnosis and evaluation of a variety of diseases that involve or cause alterations in normal vascular anatomy or physiology.
The progress in X-ray contrast media development has been extensively documented; e.g., U. Speck, “X-ray Contrast Media”, Medical Division Publication, Department of Medical Information, Schering AG; D. P. Swanson et al., “Pharmaceuticals in Medical Imaging” (1990) McMillan Publishing Co.; M. Sovak, “Radiocontrast Agents”, (1984), Springer Verlag. Preferred intravascular X-ray contrast agents possess a combination of desirable properties. Such properties include the following to various degrees: (1) maximum x-ray opacity; (2) biological safety; (3) high water solubility; (4) chemical stability; (5) low osmolality; and (6) low viscosity. In particular, studies have shown that high osmolality can be correlated with undesirable physiologic adverse reactions to x-ray contrast media, e.g., nausea, vomiting, heat and pain.
A significant advancement in the area of triiodobenzene based X-ray contrast media has been the development of non-ionic triiodobenzoic acid derivatives such as iopamidol, iohexyl and ioversol. In general, aqueous solutions of these non-ionic agents have less osmolality than previous agents and hence, provide greater patient comfort when injected. Adverse reactions, especially in the sensation of pain, warmth, and hemodynamic effects are greatly reduced as compared to the ionic triiodobenzoic acid derivatives. However, at equal iodine concentrations, the viscosity values of these non-ionic formulations are higher than for formulations of ionic triiodobenzoic acid based contrast agents.
Further reduction of osmolality of X-ray contrast media resulted from the introduction of non-ionic dimeric agents such as iotrolan and iodixanol. These agents because of isoosmolality values, as compared to the non-ionic monomeric agents, provide even greater patient comfort by reducing nausea and vomiting upon intravenous injection and by causing much less pain upon peripheral arterial injection. However, the frequency and intensity of delayed side reactions in patients are higher for such non-ionic dimers. The viscosity of such non-ionic dimeric agent-based formulations is also substantially greater than for the corresponding monomeric analogs. Thus there remains a need for safe formulations of X-ray contrast media with low viscosity and low osmolality
In U.S. Pat. No. 5,698,739 (Sovak), Sovak describes a separate class of dimeric non-ionic X-ray contrast media with at least one primary carboxamide group as a substituent, an example of this class of dimers being Iosmin. According to Sovak, the presence of primary carboxamide group conferred higher iodine content and sterically exposed the hydrophobic character of the neighboring iodine molecules ensuring the formation of aggregates and thus lowering the osmolality.
Another attempt to optimize formulations involves combining a monomer with low viscosity value with a dimer of low osmolality value wherein the substituents on the iodinated aromatic groups are similar. U.S. Pat. No. 5,695,742, discloses injectable aqueous compositions comprising mixtures of non-ionic iodinated aromatic monomers and non-ionic iodinated aromatic dimers having an intermediate osmolality value compared to the pure solutions wherein the mixtures are also disclosed as having a lower viscosity than expected.
With the purpose of decreasing the delayed side reactions seen with the non-ionic dimers, German Patent Application DE 19627309 discloses mixtures comprising monomers and dimers of ionic and non-ionic triiodoaromatic compounds as well as gadolinium complex compounds. Since the mixtures include an ionic contrast agent, the osmolality of such a mixture would be higher than the osmolality value for the pure nonionic dimer contrast agent.
We have now surprisingly discovered novel monomer-dimer mixtures having improved property, e.g. osmolality and viscosity, profiles in which the dimer has at least one primary carboxamide group in the triiodobenzene nuclei and the monomer has no primary carboxamide groups in the triiodobenzene nuclei.